Utilization of a source directly emitting a wide spectrum white light such as an incandescent lamp or a quartz lamp is already known. The direct utilization of such sources has numerous disadvantages such as, for example, the overall dimension, the isotropic emission or the weak luminance.
To obtain a wide-band white light, it has been attempted to associate in parallel a great number of mono-frequency laser diodes, but it should be understood that the spectrum is not continuous. Besides, variations in intensity may occur between the diodes.
Another known means for obtaining such a light is pumping a micro-structured optical fiber with a mono-frequency laser which works in pulsed operation, with pulses of the order of a nanosecond, a picosecond or a femtosecond for distribution frequencies between the kilo-hertz to the megahertz. It is known that such pumping induces non-linear effects in the micro-structured fiber which allow the generation of photons having various wavelengths. This type of source has been described in the publication by J. K Ranka et al., Optics Letters, Vol. 25, No. 1, p. 25-27, 2000 and in the document by J. C. Knight et. al., Optics Letters, Vol. 26, No. 17, pages 1356-1358, 2001. The disadvantages of such a source are the overall dimensions and the cost which prevents its utilization in an integrated product.
FR 04 02589, filed on Mar. 12, 2004 and not yet published, discloses, as illustrated in FIG. 1, a device comprising an optical pumping module MP in charge of providing a radiation having at least two different excitation wavelengths λI and λ2. It also comprises light guidance means GL which, when they are excited by a radiation including several wavelengths provided by the pumping module MP in a non-linear light-material interaction regime, provide a polychromatic light corresponding to a continuum at their outlet SGL.
FR 04 02589 discloses, in a mono-modal fiber using a negative dispersion regime, the pumping by a mono-frequency source gives rise to the generation of Raman discrete lines for high wavelengths. On the contrary, in the case of pumping with at least two judiciously selected wavelengths, it was demonstrated that a symmetrical homogeneous spectral spreading appeared on either side of the one the pumping wavelengths, as well as a minimization of the Raman components. This modification is mainly the result of a competition phenomenon between the non-linear effects. The spectral spreading can be explained by the combination of the phase self-modulation, the crossed phase modulation and the parametric effects (four wave mixture). The addition of a second pumping power then makes it possible to initiate initial phase matching between the wavelengths centered around λI and λ2 and the occurrence of the parametric effects which have an occurrence threshold lower than that of the Raman effect. As illustrated in FIG. 1, such a device thus comprises pumping means MP which generate two wavelengths λI and λ2 at the outlet SMP. Such radiation then goes into the guidance means GL through the inlet EGL and a wide-spectrum white light is emitted at the outlet of the guide GL through the outlet SGL.
Although FR 04 02589 already solves many problems in the field of obtaining a white light, it requires a double pumping which requires either a double pump or a frequency doubler which can be a problem.
It could therefore be advantageous to simplify the previously described device while still having satisfactory results as regards the emitted light and at making it possible to obtain a spectrum without any discontinuity.